In reissue patent application Ser. No. 965,097, "POWER ACTUATED LAMINATING MACHINE", filed Nov. 30, l978, incorporated herein by reference, a laminating system is disclosed for use with laminating packets. Each packet preferably comprises upper and lower laminating leaves such as polyethylene film with a heat reactivatible adhesive layer thereon and a cardboard tab attached at one end of the packet which is releasable such as by adhesive tape. After the packet is run through the laminating machine, the tab is then removed.
In this system, the lamination machine provided has upper and lower heating plates forming a heating zone and rearwardly of the heating zone upper and lower drive rollers are provided which form a nip for engaging the cardboard tab. Initially, an operator inserts the packet into the machine into a "ready" position. Thereafter, the operator may activate a handle on the machine which causes the heating plates to approach one another and also causes the drive rollers to engage the cardboard tab.
When the handle is engaged, the heaters come up to proper operating temperature and a thermistor is provided through a zero crossing switch which causes the heaters to turn off and on to maintain desired temperature. A drive motor is activated which causes the packet to begin moving through the machine. As the trailing edge of the packet passes a sensor, a time delay is actuated and the motor continues to operate for a sufficient length of time for the packet to completely clear the machine. The tab is then torn off the packet and the lamination operation is completed.
With this system, temperature overshoot problems occur since the heating zone temperature continues to rise despite disconnection of power after achieving an operating temperature. This temperature overshoot causes excessive heating of the packet and particularly the connection tape between the tab and the packet. Also, since the packet remains stationary while the temperature increases to operating temperature, the packet does not act as a "load" in the heating zone since typically only the lead end of the packet is present in the heating zone. Since this lead end is stationary in the heating zone, the amount of heat transfer is less than it is when the packet is moving and consequently excessive temperature rises occur.